1. Field of the Invention
The present invention relates to semiconductor modules and more particularly a packing structure that is preferable for a power semiconductor module used in a home appliance or industrial equipment.
2. Description of the Related Art
In the case of a power semiconductor element module used in home appliances or automobile control equipment or the like (for example, an insulated gate bi-polar transistor (hereinafter called as IGBT), it is general to employ a structure having the power semiconductor element connected with wirings on a high thermal conductive ceramic substrate by hot thermal conductor material such as solder and the like in order to increase a thermal radiation characteristic. However, in view of the fact that although the ceramic substrate shows a high thermal conduction, its cost is high, a structure having a metallic substrate is used, the metallic substrate having thereon wirings connected under application of resin of relative high thermal conduction efficiency to a metallic plate of Al (aluminum) or Cu (copper) and the like. When the aforesaid metallic substrate is used, it is also proposed to employ a structure having a thermal diffusion plate held between the power semiconductor element and the wiring so as to improve a thermal radiation characteristic of the power module.
Japanese Patent Laid-Open No. 2001-110957 (Japanese Patent No. 3627591) (Patent Document 1) discloses a method for manufacturing a power semiconductor module using the metallic substrate. In accordance with this Patent Document 1, both a semiconductor chip 1 and a thermal diffusion plate 3 are connected by hot solder 105 of a melting point of 270° C. or higher within a reducing atmosphere furnace. A lead frame 2 and an electrode surface are also connected with a hot solder 104. Thereafter the thermal diffusion plate 3 and a first conductive layer (film) 41 on the wiring substrate are connected by a solder 106 of low temperature, and the lead frame 2 and a second conductive layer (film) 42 on the wiring substrate are connected by a solder 107 of low temperature (see FIG. 8). According to the structure described in Patent Document 1, since the lead frame 2 is used as the wiring, the electrical resistance value of the wiring can be reduced. In addition, Patent Document 1 describes that a wire bonding can be eliminated because the lead frame 2 is connected by solder within the reducing atmosphere furnace, and that the lead frame 2 can assist a function of the thermal diffusion plate.